Multi-channel communications links are important components of various computing platforms, including the S/390 and RS/6000 Power Parallel Systems offered by International Business Machines Corporation. One example of a multi-channel communications link is the Self-Timed Interface (STI) data link offered by International Business Machines Corporation. The STI data link is conventionally a bidirectional parallel data bus comprising multiple DC differential wire pairs. Because of the DC coupling, testing of the wires is relatively straightforward.
In certain enhanced computing platforms, such as the Z/990 eServer System offered by International Business Machines Corporation, the self-timed parallel interface is implemented by multiple AC differential wire pairs. With AC differential wire pairs, the drivers and receivers on opposite ends of the interface are capacitive coupled. Such a system is referred to herein as an Enhanced Self-Timed Interface (ESTI). Because of the capacitive coupling, a receiver may under certain circumstances detect a received signal even when one of the true or complement wires of the corresponding differential wire pair is open circuited or shorted to ground. Without a test to detect open or short circuited wires, the ESTI link may initialize and become operational only to run with an unacceptable bit error rate.
With the migration to ESTI links, therefore, there is a need for testing integrity of the multiple AC differential wire pairs of the enhanced self-timed parallel interface, as well as a need for an initialization approach for the enhanced self-timed parallel interface, and an approach for bringing the parallel interface down when required. The present invention is directed to addressing these needs.